Methods and Apparatus for Random Access in Multi-Carrier Communication Systems

1. In a multiple access wireless communication system having a plurality of base stations covering a plurality of cells, a method by a base station to determine a time delay associated with a mobile station using a random access subchannel, the method comprising: allocating, within a communication channel, a random access (RA) subchannel selected from a plurality of frequency subchannels and a RA time slot selected from a plurality of time slots, the RA time slot and RA subchannel associated with the cell in which the base station is located; receiving a signal from a mobile station over the selected RA subchannel in the selected RA time slot; processing the received signal by: applying a Fast Fourier Transform (FFT) to the received signal to generate a transformed signal in the frequency domain; computing, in the frequency-domain, a dot-product between the transformed signal and an RA sequence specific to the cell in which the base station is located; analyzing the computed frequency-domain dot-product to identify the RA sequence carried in the received signal; computing, in the time-domain, a correlation between a time-shifted version of the received signal and the identified RA sequence; and analyzing the computed time-domain correlation to determine a time delay associated with the mobile station; identifying the mobile station associated with the RA sequence; and transmitting to the identified mobile station an indication of a time advance based on the determined time delay associated with the mobile station.

2. The method of claim 1 , wherein the RA subchannel is comprised of subcarriers that are contiguous in frequency.

3. The method of claim 1 , wherein processing the received signal further comprises computing, in the frequency-domain, a dot-product between the transformed signal and a second RA sequence specific to the cell in which the base station is located.

4. The method of claim 1 , wherein analyzing the computed frequency-domain dot-product to identify the RA sequence carried in the received signal comprises comparing a value of the computed frequency-domain dot-product with a threshold value.

5. In a multiple access wireless communication system having a plurality of base stations covering a plurality of cells, a base station configured to communicate with a mobile station over a random access (RA) subchannel selected from a plurality of frequency subchannels and a RA time slot selected from a plurality of time slots, the RA time slot and RA subchannel associated with the cell In which the base station is located, the base station comprising: a receiver configured to: receive a signal from a mobile station over the selected RA subchannel in the selected RA time slot; and a processor configured to process the received signal by: applying a Fast Fourier Transform (FFT) to the received signal to generate a transformed signal in the frequency domain; computing, in the frequency-domain, a dot-product between the transformed signal and an RA sequence specific to the cell in which the base station is located; analyzing the computed frequency-domain dot-product to identify the RA sequence carried in the received signal; computing, in the time-domain, a correlation between a time-shifted version of the received signal and the identified RA sequence; analyzing the computed time-domain correlation to determine a time delay associated with the mobile station; and identifying the mobile station associated with the RA sequence; and a transmitter configured to transmit to the identified mobile station an indication of a time advance based on the determined time delay associated with the mobile station.

6. The base station of claim 5 , wherein the RA subchannel is comprised of subcarriers that are contiguous in frequency.

7. The base station of claim 5 , wherein, to process the received signal, the receiver is further configured to compute, in the frequency-domain, a dot-product between the transformed signal and a second RA sequence specific to the cell in which the base station is located.

8. The base station of claim 5 , wherein analyzing the computed frequency-domain dot-product to identify the RA sequence carried in the received signal comprises comparing a value of the computed frequency-domain dot-product with a threshold value.

9. The method of claim 1 , wherein the frequency-domain dot-product is computed in a segment-wise fashion.

10. The method of claim 1 , wherein the time-domain correlation is computed in a sliding-window fashion.

11. The base station of claim 5 , wherein the frequency-domain dot-product is computed in a segment-wise fashion.

12. The base station of claim 5 , wherein the time-domain correlation is computed in a sliding-window fashion.